Reproduction of sound



1,39,713 Augc 239 1927 A. F. SYKES REPRODUGTI ON OF SOUND Original Filed Nov. 16. 1920 2 Sheets-Sheet I mvmzmoa: 7 A. F. SYKES,

By his Attorney, 047% Aug, 23, 19270 19639y713 A. F. SYKES REPRODUCTION OF SOUND Original Filed Nov. 16, 1920 v 2 51 1 41 2 V INVENTOR: A. F. smas,

By his Attorney Patented Aug. 1927.

UNITED STATES 1,639,713 PATENT OFFICE.

ADRIAN FRANCIS SYKES, OF NEW BARNET, ENGLAND.

' aarnonuc'rron or social).

original application iiled November 16, 1920, Serial No. 424,421, and iii-Great Britainll'ovember 18, 1819.

Divided and this application filed April 10, 1824. Serial No. 705,713.

This invention relates to apparatus for the conversion of sound into equivalent variation of electric currents or potentials and to the conversion of electric currents or derivatives thereof into mechanical vibration for the purpose of reproduction.

This ap lication is a division of my application erial No. 424,421, filed Nov. 16, 1920.

The primar object of my invention is the production 0 phonograph or gramophone records of improved fidelity inwhich tonal purity, definition and beauty are enhanced while disturbances, false tones and blasts are minimized and in general in which defects usually attributed to the natural tones of diaphragms and the resistance of the wax to impression are eliminated.

In the full practice of my invention I employ a primary detectorof a non-resonant nature which serves to derive electric potentials from sound waves, a system for modifying or distorting the wave forms ofthe potentials so derived and a powerful thermionic relay for the purpose of amplifying the efiects in order that they may be large enough to operate a special recording device which is either in fact or in effect non-resonant. Sound is caused to vibrate a collecting mass of material either in fact or in effect devoid of tones and a coil immersed ina magnetic field or a microphone serves to detect the vibration; the electric currents derived in this way are distorted by means of the thermionic valve and inductances or by a condenser system or by both in combination; the distorted currents are then circulated in an inert coil of wire situated in a magnetic field to which coil is attached an engraving jewel in contact with a wax blank. The distortion required depends on circumstances as will be evident later. It is sometimes desirable to make use of a mechanical system with one tone or period of vibration and to make provision for eliminating the infiuence of this tone as will be described.

It will be convenient to deal with the problem of the derivation of electric currents equivalent to sound waves or systemab ically difiering therefrom and the problem of engraving mechanical equivalents of electrical oscillations or systematic derivatives thereof separately and then to make some remarks on their use in combination.

Thus as regards detection my invention consists in allowing sound to vibrate a plain szamplitu-de of vibration a=acceleration f=frequency the expression for the acceleration is (1 s G=EF= 4:Il'%f 8 I define a plain mass as a body so supported and free from external or internal constraint that it would require a force of M times 411- f s to cause it to execute this 7 vibration. A diaphragm of mass M does not n general for the purpose of this specification constitute a plain mass since any tones it possesses require much less force of the same frequency or nearly the same frequency to excite to a given amplitude than corresponds to the above formula. For the purpose of this specification the reaction of the supports necessary to maintain the mass n position relative to the other apparatus 1S neglected since the constraint is trivial compared with the inertia of the mass itself; A plain mass has now been described technically; it will be observed that it does not preclude a composite nature for the body employed. Wherever in the specification and claims the term plain mass is employed, it is to be understood as having a meaning above, defined.

Mathematically if the mass is acted upon by the pulsatory force of sound the amplitude of vibration to each harmonic is inversely proportional to the square of the frequency of the particular harmonic, and the maximum velocity attained is inversel proportional to the frequency, hence the M. F. generated in the coil falls uniformly as the frequency rises. If now this E. M. F. is applied to an apparatus. capable of enlarging every harmonlc in the proportion of its frequency the root mean square value of the current or' potential so attalned 1s a constant quantity. The harmonics referred to are harmonics of pressure on the body. At this stage it may be observed that wlthout any modification the coil enerates true electrical equivalentsof the or inate of particle displacement. Preferably the detector so defined is mod fied so that although the actual body v1 brated may not in fact be free ,from mechanical tones in efiect it behaves as though it were. Thus the coil is no longer attached to a heavy inert body but instead is wound ancake fashion, that is, a single or multii ayer spiral the turns of which are bonded together with gum, shellac or other bind ng material. With advantage the magnetic a r gap can be made large and might be SIX centimetres or even more. The coil is either hung in the gap or fastened across it by tissue paper or other tenuous membrane. Two definite conditions arise and an intermediate stage. In the first place if the weight of the I coil is so great that next to no sound is transmitted by it to the air beyond, the voltage generated is the equivalent of the displacement curve; in the second place if the coil is so tenuous, it might be composed of gold leaf, that it does not sensibly obstruct the sound the excess pressure wave is repro duced; in the third place if the coil is of intermediate weight, then for high frequencies the displacement wave is represented, for low frequencies the excess pressure wave is represented, while for intermediate frequencies something between the two occurs.

Any overtones in a coil used in this fashion must in the main be obliterated by the averaging process which takes place, that is why the coil acts as a body devoid of overtones .and conforms to the idea of a plain mass.

An apparatus with the property of enlarging every harmonic in proportion to its frequency that is of obtaining the electrical equivalent of mathematical differentiation can be constructed in the following fash- 7 taken to avoid the use of any iron core in such fashion as to distort the result by the influence of hysteresis or eddy currents. A device of this nature cannot be loaded or in other words cannot supply more than a trivtion of a non-resonant detector and a diagram of connections. Figure 3 is a rear elevation of a non-resonant sound detecting element with attached coil. Figure 4 is a fragmentary sectional view of a non-resonant detector showing a variation in "construction. Figure 5 is a fragmentary section of a detector with pancake coil of wire which detector is in effect non-resonant.

Figure 1 shows a plain mass 1 of com osite construction built up from a disc of e onite 2, a sheet of india rubber 3 and'more ebonite 4 cemented together; a former or frame 5 carries a coil of wire 6 immersed in the field between the poles 7, 8 and 9, of the electromagnet 10, with a winding 11. The plain mass 1 is supported by ligaments, light springs or the like, in an aperture in a wall 12, shown in section, from which it is separated by a space 13 usually made very small. To operate the apparatus sound is produced on the side of the Wall remote from the electroma et. A convenient arrangement is to ma e the wall 12 a division between two rooms, one the recording room and the other the instrument room. A horn or trumpet may if desired be used to concentrate the sound waves upon the mass 1.

Figure 2 is a fragmentary view in part section of the elevation of Figure 1. The ligaments 14 attached to projections 15 in the wall and plain mass respectively are shown supporting the mass. Terminals 16 receive wires from the coil 6. Across these terminals are placed a non-inductive resistance 17 and a condenser 18. Between the terminals 19 is felt the voltage variation across the non-inductive resistance 17. A number of valve relays in cascade are interposed between the terminals 19 and the terminals 20 so that the plate current in the last of the series is carried by the wires from the terminals 20 and this plate current is an enormous magnification and replica of the potential across the terminals 19; this plate current is caused directly or indirectly to operate a receiving or recording telephone.

Figure 3 is a view of the coil 6 wound on its former 5 at the rear of the plain mass and 8 of the electromagnet are of the peg and ring type, that is the pole 7 encircles the pole 8 and the field is radial. In this construction the pole 7 is built into and forms part of the recording Wall 12. The primary detector orplain mass 1 is of conical shape andmade from ebonite; the coil 6 is wound on the periphery of the detector.

Figure 5 is a View of another form of primary detector constructed according to the invention. In the annular space between the poles 33 and 34 of a powerful electromagnetis located the detecting coil 29, 32, mounted on the tissue paper or india rubber membrane 49. As a refinement a similar or approximately similar coil 50 is mounted on the ebonite ring 51 perforated with holes 52. The coils 29. 32 and 50, are connected in series or parallel'in such a manner that the inductance of the two coils becomes practically nothing as in Dr. Drysdales wattmeter (see Alternating Currents-Hay, 1907). The coil, however, only has to supply the grid current and as that is usually very small indeed the compensating coil is not essential. Sound is produced on the side of the wooden wall 31 remote. from the magnet, which Wall 31 may be one side of a box inclosing the apparatus or simply a partition between two rooms. A rubber ring 521 intervenes between the encircling pole 33 and the partition 31. The detecting coil 29, 32, responds to the pressure wave and generates E. M. F. proportional to the ordinate of the displacement wave of the incident sound. This E. M. F. is brought to' the terminals 35 and 36.

What I claim is 1. In means for reproducing sound, means for producing a magnetic field, a material body free from natural frequencies over the important acoustic range, a winding arranged to move with the said body and su ported in said field in such a way as to e controlled by mass alone in the acoustic sense. I

2. In means for reproducing sound, means for producing a magnetic field and a, conducting sheet immersed therein and unconstrained in an acoustic sense by edge fixation and adapted to be vibrated by the ,direct action of sound acting over the whole of one exposed side of the sheet.

3. In means for reproducing sound, means for producing a magnetic field, a conducting sheet of annular form immersed therein and a support for the sheet, the fundamental natural period of vibration of the sheet with respectto the support being so low that it is of no acoustic importance.

4. In means for reproducing sound. means for producing a magnetic field, a conducting sheet immersed therein and unconstrained in an acoustic sense byedge fixation and adapted to be vibrated by the direct action of sound acting over the whole of one exposed side of the sheet and a fixed series conducting sheet so arrangedthat the field due to a circuit in the fixed sheet is opposed to the field due to the current in the movable sheet.

5. In means for reproducing sound, means for producing a magnetic field, a conducting sheet of annular form immersed therein, a support for the sheet, the fundamental natural period of vibration of the sheet with respect to the support being so low that it is of no acoustic importance, and a fixed series conducting sheet so arranged that the field due to a currentinthe fixed sheet is opposed to'the field due to the current in the movable sheet.

6. In means for reproducing sound, the combination of means for producing a magnetic field, a tenuous conducting film v1- bratable by sound waves and located in the magnetic field and means for obtaining a current or potential from the movements of the film.

7. In means for reproducing sound, the combination of means for producing a magnetic field, a conducting body vibratable by sound waves and located in the magnetic field and means for obtaining a current or potential from the movements of the body,

the body being not itself free from tones but so arranged that sectional vibration of the body has substantially no effect on the action of the apparatus.

8. In means for reproducing sound, the combination of a field magnet giving an annular field, an annular sheet suspended in the field and a winding distributed over substantially the whole of the sheet.

9. In means for reproducing sound, the combination of a. field magnet producing an annular field, a thin annular sound responsive body located in the magnetic field, a conductor carried'by the annular body, and a Winding for energizing the field magnet in rear of the annular body, the sound waves having direct access to the face of the annular body remote from the winding.

10. In means for reproducing sound, the combination of a. field magnet producing an annular field, an annular sheet suspended in the field and a conductive winding distributed on the sheet.

11. In means for producing sound. means for producing a magnetic field. a plain mass immersed in said magnetic field and adapt-ed to be vibrated by sound waves, and means for obtaining a potential or current from the movement of said mass.

12. In means for reproducing sound, a material body free from natural frequencies over the important acoustic range. a windinqarranged to move. with the said body and supported in such a way as to be controlled by mass alone in the acoustic sense, and a magnet producing a field engagin with the winding, whichwinding is suspen ed in and distributed over substantially the whole of the air gap of the said magnet.

13. In means for reproducing sound, a material body free from natural frequencies over the important acoustic range, a Winding arranged to move with the said body and supported in such a Way as to be controlled by mass alone in the acoustic sense, a magne'tic field engaging with the winding, and

means for causing currents of acoustic signlficance to circulate in the sald wmdmg.

14. In means for reproducing sound, a

magnetic field, a conducting sheet immersed =therein and unconstrained in an acoustic :sense by edge fixation, and means for 'caus-' "mg currents of acoustic slgmficance to circulate in the said conducting sheet.

15 .In means for reproducing sound, means for producing a magnetic field, a plain mass immersed in said magnetic field, and. means for causing currents of acoustic "significance to circulate in the said mass;

In testimony that I claim the foregoing as my invention I have signed my name this 1st day of April, 1924.

' ADRIAN FRANCIS SYKES. 

